Given the error codes in the absence of anything else, the fact that presumably everything was working fine for some lengthy time previously and the PC wasn’t dropped or jolted recently (you would have mentioned it) and you state you managed to get all the modules working with nothing more than a remove and re-insert (no BIOS reset to defaults) I’d suggest it was either a poor contact module pin or a transient glitch (power surge, static, etc.) Only other issue could be an EXPO setting (you don’t mention if timings set or at default) that may have once worked fine on a new board and ram but as it stuff has aged the hardware may not be what it once was (aren’t we all ?) and the BIOS may benefit from a small tune down if EXPO was set.

However E3/E5 on that board suggests a DRAM detection and training initialisation issue. How hot and sticky is it there in Argentina ? I see at around this time of year can be 70-78% which is high enough to cause issues on pins so is the PC in an air-conditioned room or do you use a dehumidifier ? Anyway I suspect some slight oxidisation corrosion build-up on a module somewhere which eventually could have caused the issue with the heating and cooling when switching the PC on and off. By removing and reinserting them one at a time you likely scraped any minor corrosion away.

If me I would have probably just cleaned with isopropyl alcohol and inspected the pins closely and then run Memtest for a couple of hours or even overnight to give the modules a damn good thrashing but maybe it’s all good without the extra effort. I’d recommend backing up data often in the meantime until you are sure ! Can’t have you losing the next week’s DCT article !